1. Field of the Invention
The present invention relates to retrofocus type standard lens and wide angle lens.
2. Description of Related Art
In a conventional focusing system of a lens, there are entire advance type in which the lens groups are entirely moved upon focusing, and floating types in which the front and rear lens groups are independently moved to vary the distance between the lens groups upon focusing. However, in either type, since the diaphragm unit is also moved during the focusing, it is difficult to simplify the structure of the lens barrel.
There is also known a front lens advance type in which only the front lens group is moved without moving the diaphragm. To simplify the lens barrel, it is desirable to use a front lens advance type to thereby restrict the aberration. To this end, it is necessary to reduce the absolute value of the aberration factors of the front lens group and the rear lens group. However, in the conventional retrofocus type lenses, it is difficult to restrict the aberration fluctuation during the focusing.